1. Field of the Invention
The present invention relates to a cap having a function for enabling a wearer to see or hear various information including images, characters, voices, and the like.
2. Description of the Related Art
A typical cap with a display function is configured to arrange a number-display element that functions as a clock in a visor at an oblique or approximately horizontal angle, and to form a virtual image of the display element by use of a concave mirror arranged to cover the eyes of a wearer, thereby allowing the wearer to see the virtual image.
A typical head mount display is configured to arrange a prism block including a concave mirror in front of the eyes of a wearer, and to form an enlarged virtual image that is derived from a display element positioned beside the prism block by use of the concave mirror, thereby allowing the wearer to see the virtual image (See for example, U.S. Pat. No. 5,739,797).
In the prior cap with a display function described above, light from the display element enters the concave mirror at a shallow angle. Accordingly, a planar shape of the concave mirror is formed into an aspheric shape, a nonaxisymmetric shape or the like for aberration correction, thereby optimizing the display image. However, it is difficult to achieve fine aberration correction throughout a wide field of view and to realize image display at high resolution and with a wide view angle.
Similarly, in the above-described prior head mount display, light from the display element enters the concave mirror at a shallow angle. Correspondingly, an incident surface of the prism block for the light from the display element is formed into an aspheric shape, and the concave mirror is formed into a nonaxisymmetric shape to achieve fine aberration correction throughout a wide field of view. Accordingly, such a device is heavy and expensive to manufacture. This device also has a disadvantage in that an image is apt to partly vanish as a result of eye movement.
Meanwhile, when the concave mirror in any of the foregoing configurations includes a translucent mirror, the concave mirror creates a distorted outside view. Accordingly, the wearer cannot observe a clear view when superimposing the display image on the outside view.